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      >> Introduction 
      >> Layout and Setup Tips 
      >> Focus Block Replacement 
      >> CRT Tube Replacement 
      >> Manuals / Downloads 



The Zenith PRO 840 and the later and improved PRO 851 (and PRO 890 with a built in tuner) are what I consider to be the most reliable and inexpensive CRT projectors ever made. I’ve installed literally 100s into sports bars that run these 14 hours a day, 7 days a week, and still continue to retube these projectors. Despite their somewhat sloppy wiring and haphazard board construction, these convection cooled sets work very well for non-critical video only applications. Many home theaters also have a PRO 851 installed due to the low initial retail price (typically under $3500 USD).

These are video only units with one composite video input. 750 lumens from 7" tubes, modular construction, on screen menus, analog convergence.

There are a lot of pros and cons with the PRO 851. Due to the low selling price, Zenith cut some corners on the set to keep the costs down. The set uses cheap acrylic lenses with only one master focus control. This gave the set worse corner focus than other 7” ES focusing sets. These lenses also have a unique short throw distance of 1.2 X the width of the screen as compared to 1.4 X the width of the screen for most other sets. Therefore, if you want to upgrade from the PRO 851, you need to move the new projector back somewhat to attain the screen size. The higher end PRO 900 projector will mount within inches of the PRO 851, but the PRO 900 uses the same cheap lenses for the same focus limitation of the entry level set. The overall picture of the PRO 851 is still great for sport bar and non critical viewing however.

The Zenith installation and user manual is not very well written. The download found in this section for the Runco 750 is the best written manual that I’ve found. Zenith made this set for a number of other companies including Runco, GE, Knoll, Ampro, and anyone else that had enough funds to buy 200 projectors at a time. Zenith would OEM this set by taking the Zenith stickers off of the set and the remote, and other ‘manufacturers’ would then put their own company stickers on the basic set. Some manufacturers would do minor modifications to the Zenith chassis, but none made changes that greatly improved the basic image.

While Zenith made an S-video adapter kit for this projector, the quality of the S-video input was usually worse than the composite, and Zenith didn’t sell a lot of S-video adapter boxes as a result. The RGB input connector under the green lens was a ‘future input’ that Zenith figured could be used down the road, but to the best of my knowledge never made any use of it. Line doublers and computers cannot be connected to this flat connector.

Ampro did manufacture a 1200 model that was based on the PRO 851, but Ampro literally gutted the set and modified the base 851 heavily to accept a line doubled RGB input. The inside of the set has very little in common with the PRO 851 other than the tubes and the power supply, as virtually all of the other boards were made by Ampro.

The Zenith projector was designed as a low end CRT projector, and does not have any fault or diagnostic indicators built into the set as other higher end projectors do. There is no internal test pattern generator in the unit either, when setting the projector up an external crosshatch generator or DVD must be used to align the convergence.

The Zenith PRO 851 uses analog convergence controls found under the top cover to align the three tubes. When dialed in carefully, the convergence was stable and accurate enough to use over a long period of time. Again, the Runco manual found on this site guides you through the setup procedure nicely. Note that there is no test pattern generator built into the Zenith unit. You need to use an external test generator or use the test patterns found on the AVIA test disc for a crosshatch pattern source.

Zenith didn’t really have a service manual for this set either. The total documentation consists of one large page that has the schematic on one side, and the location of each board on the other. Zenith always based their servicing on board replacement, so there are no voltage measurements or scope waveforms on the schematic. Over time I’ve gotten quite good at repairing the individual boards as Zenith has now discontinued a lot of them. All tubes have long been discontinued, but VDC still rebuilds these tubes for under $200 each. I’ve had excellent results with the rebuilds in this set.

To see how these projectors rank in relation to other projectors for use in a home theater environment see the Projector Rankings page.

For full specifications on these and other projectors, see the Projector Specifications page.

For an overview and history of Zenith see the CRT Primer.

See the Advanced Procedures page for various DIY instructions on maintaining and improving CRT projectors.

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